St. Paul states: “For all of you who were baptized into Christ have clothed yourselves with Christ.” What does this mean? St. Thomas explains that we “put on Christ” through “a likeness and configuration of the death of Christ.” St. Thomas refers to the Letter to the Romans, “We who are baptized in Christ Jesus are baptized in His death” (Rom 6:3).
Thomas points out that the act of baptism in itself is not effective without faith: “For baptism comes about only through faith, without which we derive no effect from baptism: ‘He who believes and is baptized shall be saved; but he who does not believe shall be condemned’ (Mk 16:16).”
St. Thomas compares putting on Christ with putting on clothing:
Here it should be noted that when someone puts on clothing he is protected and covered by it and his appearance is that of the color of the clothing instead of his own. In the same way, everyone who puts on Christ is protected and covered by Christ Jesus against attack and against the heat; furthermore in such a one nothing appears except what pertains to Christ: ‘Put on the Lord Jesus Christ’ (Rom 13:14).
St. Thomas compares putting on Christ with burning wood:
Again, just as burning wood takes on fire and shares in fire’s activity. So he who receives the virtues of Christ has put on Christ: ‘Stay in the city until you are clothed with power from on high’ (Lk 24:49). This applies to those who are inwardly clothed with the virtue of Christ: ‘Put on the new man, who according to God is created in justice and holiness of truth’ (Eph 4:24). And note that some put on Christ outwardly by good works and inwardly by a renewal of the spirit; and with respect to both they are configured to His holiness…
St. Paul declared that there are no differences between people, such as Jew or Greek, slave or free, male or female: “For all are one in Christ Jesus” (Gal 5:28). St. Thomas comments:
Truly, none of these things makes a difference in Christ, because all of you, i.e. believers, are ‘one in Christ Jesus,’ because through baptism you have been made members of Christ and you form one body, even though you are distinct individuals: ‘So, we being many, are one body in Christ, and everyone members of one another’ (Rom 12:5); ‘One body, one Spirit, as you are called in one hope of your calling’ (Eph 4:4). Now where there is unity, difference has no place. Indeed it was for this unity that Christ prayed: ‘That they may be one, as one, as You, Father, in me, and I in You’ (Jn 17:21).”
Denis Vincent Wiseman, O.P.
The quotations from Thomas Aquinas are from Thomas Aquinas, Commentary on Saint Paul’s Epistle to the Galatians, translated by F. R. Larcher, O.P., (Albany, NY: Magi Books Inc., 1965), pp. 18-31.